Field effect transistors (FETs) that are based on inorganic materials such as silicon (Si) are well-known and widely used. A typical FET device includes several layers, such as a substrate layer, a semi-conductor layer, source and drain electrodes connected to the semiconductor layer, a gate electrode, and an insulator layer between the gate electrode and the semiconductor layer. Applying a potential to the gate electrode results in charge carrier accumulation or depletion at the interface of the semiconductor layer and insulator layer, depending on the applied gate voltage and the semiconductor material type. When charge carriers are accumulated at the interface, a conductive channel then formed between the source and the drain electrodes and current flows when a potential is applied to the drain electrode. On the other hand, when charge carriers are depleted at the interface, current cannot easily flow between the source and drain, and the transistor is considered to be “off.”
There has been a growing interest in developing FETs using organic materials to produce an organic thin film transistor (OTFT). Mobile electronic applications usually use a battery as a power source and need small power consumption electronic systems to prolong battery life. However, OTFTs developed thus far need high driving voltages, which causes large power consumption and undesirably short battery life. This is at least partially due to the limited capacitance value (typically, Ci<100 nF/cm2) of the dielectric materials in OTFTs. Much work has been done to obtain large capacitances of dielectrics for OTFTs, including employing high-dielectric-constant (high-k) metal oxides such as Ta2O3, TiO2, and the like, and using ultra-thin polymer or self-assembled monolayer (SAM) dielectrics. However these materials still have limited capacitance values (Ci<1 μF/cm2).
Additionally, polymer electrolytes have been studied as an alternative insulating layer because of their high capacitances, typically greater than about 10 μF/cm2. Devices based on polymer electrolytes can be operated at low voltages with much higher output currents. However, devices based on polymer electrolytes are limited in terms of transistor switching frequency, and typically have a maximum operating frequency of less than about 50 Hz. While not wishing to be bound by any specific theory, it is believed that this low switching frequency results from the very low ionic conductivity (on the order of 10−4 to 10−5 S/cm) of polymer electrolytes, which limits polarization frequency, and thus switching speed.